WO2018230683A1

WO2018230683A1 - Coated paper for use in printing

Info

Publication number: WO2018230683A1
Application number: PCT/JP2018/022836
Authority: WO
Inventors: 詩織柿木; 遼外岡; 吉松　丈博; 清畠山
Original assignee: 日本製紙株式会社
Priority date: 2017-06-15
Filing date: 2018-06-15
Publication date: 2018-12-20
Also published as: TWI781183B; JP7123926B2; JPWO2018230683A1; TW201920809A

Abstract

Provided is a coated paper for use in printing, comprising two or more pigment coated layers on at least one surface of a base paper, the outermost pigment coated layer containing calcium carbonate having a mean particle size (D50) of 0.80 µm or less. This coated paper for use in printing has both print glossiness and exceptional ink drying, and also has exceptional print quality.

Description

Coated paper for printing

The present invention relates to a coated paper for printing having both ink drying properties and printing glossiness.

Coated paper is broadly divided into glossy coated paper and matte coated paper. Glossy coated paper includes art paper, super art paper, and coated paper used for catalogs, brochures, etc., which were conventionally used for high-grade printing, and these have a high gloss and printing gloss. Glossy.

Matte coated paper is coated paper that has a lower white paper gloss or printing gloss than gloss coated paper, and includes dull coated paper and matte coated paper. In particular, the demand for matte coated paper has increased in recent years because the difference between the glossiness of blank paper and the printed glossiness is larger than that of glossy coated paper, and the character portion after printing is easy to read. As a method of manufacturing matte coated paper, use of a pigment having a large particle diameter as a coating pigment, or a method of increasing the unevenness of the paper surface by not performing a calendar treatment after pigment coating. Is mentioned. Matte-printed coated paper has larger surface irregularities than glossy coated paper, and ink on the surface of the paper tends to sink. In order to increase the printing density, it is necessary to transfer a large amount of ink. Therefore, the coated paper for matte printing tends to have a large amount of ink transfer and a decrease in ink drying property. Inferior ink drying properties may cause problems such as ink transfer to the other side when the printed matter after printing is overlaid, rubbing stains on the printed surface, and work efficiency not being able to proceed to the next process. To do. For this reason, high ink drying properties are required particularly for coated paper for matte printing.

On the other hand, if the ink drying property is high, leveling of the printed ink surface does not progress, and irregularities are formed on the printed surface, often resulting in low print gloss. As a technique for increasing the print glossiness, there is a method of pursuing smoothness by calendar processing. However, since the glossiness of the white paper increases with the glossiness of printing, it is not suitable for coated paper for matte printing. In order to achieve both high ink drying properties and high printing gloss, Patent Document 1 discloses the use of a specific amount of a specific adhesive in the pigment coating layer.

JP 2007-51388 A

An object of the present invention is to provide a coated paper for printing, in particular, a coated paper for matte printing, which has both printing glossiness and excellent ink drying properties and is excellent in printing quality.

In view of the above problems, the present inventor has conducted sincerity studies, and as a result, has found that a coated paper for printing provided with a pigment coating layer containing specific fine calcium carbonate solves the above problems. That is, the said subject is solved by the following this invention.
(Aspect 1) At least one side of the base paper is provided with two or more pigment coating layers,
A coated paper for printing, wherein the outermost pigment coating layer contains calcium carbonate having an average particle size (D50) of 0.80 μm or less.
(Aspect 2) The coated paper for printing according to aspect 1, comprising 40 parts by weight or more of the calcium carbonate in 100 parts by weight of the pigment in the outermost pigment coating layer.
(Aspect 3) The coated paper for printing according to Aspect 1 or 2, wherein the calcium carbonate has an average particle diameter (D50) of 0.50 to 0.75 μm.
(Aspect 4) The coated paper for printing according to Aspect 1, wherein the glossiness of the white paper is 40% or less, and the printing glossiness of the indigo printing portion is 58 to 75%.
(Aspect 5) The coated paper for printing according to aspect 2, wherein 75 parts by weight or more of the calcium carbonate is contained in 100 parts by weight of the pigment in the outermost pigment coating layer.
(Aspect 6) The printing paper according to any one of Aspects 1 to 5, wherein the coating amount of the outermost pigment coating layer is larger than the coating amount of the innermost pigment coating layer.
(Aspect 7) The coated paper for printing according to any one of Aspects 1 to 6, wherein the glossiness of white paper is 40% or less.

According to the present invention, it is possible to provide a coated paper for printing, in particular, a coated paper for matte printing, which has both excellent printing glossiness and excellent ink drying properties and excellent printing quality.

Hereinafter, the present invention will be described in detail. In the present invention, “˜” includes its end points. That is, “X to Y” includes the values of X and Y. “X or Y” means one or both of X and Y.

1. Coated paper for printing The coated paper for printing is a paper for printing provided with a pigment coating layer provided on a base paper. A pigment coating layer is a layer which has a white pigment as a main component. The printing coated paper of the present invention contains calcium carbonate having an average particle diameter (D50) of two or more pigment coating layers and an outermost pigment coating layer of 0.80 μm or less. The coated paper for printing of the present invention can be subjected to commercial printing such as offset printing, gravure printing, on-demand printing (laser method, ink jet method, electrophotographic method), etc. on the paper surface. Examples include, but are not limited to, magazines, posters, envelopes, and calendars.

(1) Pigment coating layer 1) Pigment The pigment coating layer contains calcium carbonate having an average particle size (D50) of 0.80 μm or less (hereinafter also referred to as “first calcium carbonate”). D50 is a 50% volume average particle size. The particle size distribution and D50 of the pigment by the precipitation method can be measured with a master sizer 3000 manufactured by Malvern. The upper limit of D50 of calcium carbonate is preferably 0.75 μm or less, and preferably 0.70 μm or less. The lower limit is preferably 0.50 μm or more.

When the pigment coating layer is present on both sides of the base paper, the outermost pigment coating layer on at least one side may contain the first calcium carbonate.

The lower limit of the amount of the first calcium carbonate in the outermost pigment coating layer is preferably 40 parts by weight or more, preferably 45 parts by weight or more, in 100 parts by weight of the pigment in the pigment coating layer. preferable. However, if the amount of the first calcium carbonate in the outermost pigment coating layer is too large, the glossiness of the white paper is excessively increased and the matte tone is impaired, so the upper limit is in 100 parts by weight of the pigment in the pigment coating layer. 70 parts by weight or less, more preferably 60 parts by weight or less, and even more preferably 55 parts by weight or less. The pigment coating layer other than the outermost coating layer may not contain the first calcium carbonate, but when it is contained, the amount is preferably in the above range. The first calcium carbonate is preferably heavy calcium carbonate or light calcium carbonate produced in the causticizing step of the pulp production step (causticized light calcium carbonate, see Japanese Patent No. 5274077).

As the white pigment other than the first calcium carbonate in the pigment coating layer, a pigment usually used in this field can be used. Examples include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, satin. Examples thereof include inorganic pigments such as white and organic pigments such as a solid type, a hollow type, and a core-shell type. You may use these pigments in combination of multiple types.

As the white pigment other than the first calcium carbonate, it is preferable to use heavy calcium carbonate or light calcium carbonate (hereinafter also referred to as “second calcium carbonate”) having a D50 exceeding 0.80 μm. Since calcium carbonate has excellent binding properties with an adhesive (binder) and improves whiteness, it can improve ink drying properties and achieve higher whiteness and printability. In 100 parts by weight of the pigment in the outermost pigment coating layer, the total amount of the first and second calcium carbonates is preferably 90 parts by weight or more, and more preferably 100 parts by weight. The total amount of the first and second calcium carbonates in the other pigment coating layers is not limited, but is preferably in the above range. The second calcium carbonate is preferably heavy calcium carbonate or causticized light calcium carbonate.

2) Adhesive The pigment coating layer contains an adhesive (binder) as a matrix. The adhesive is not limited, and a known adhesive can be used. Examples include styrene / butadiene copolymers, styrene / acrylic copolymers, ethylene / vinyl acetate copolymers, butadiene / methyl methacrylate copolymers, vinyl acetate / butyl acrylate copolymers, anhydrous Latex such as maleic acid copolymer, acrylic acid / methyl methacrylate copolymer; polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol; casein, soybean Proteins such as protein and synthetic protein; oxidized starch, positive starch, urea phosphated starch, etherified starch such as hydroxyethyl etherified starch, starch such as dextrin; carboxymethylcellulose, hydroxyethylcellulose, hydride Cellulose derivatives such as carboxymethyl cellulose and the like. These multiple types can be used in combination.

The amount of the adhesive is preferably 5 to 30 parts by weight and preferably 8 to 25 parts by weight with respect to 100 parts by weight of the pigment in the total pigment coating layer from the viewpoint of printability and coating suitability. More preferred. When the total amount of the adhesive exceeds 25 parts by weight, the viscosity of the pigment coating solution becomes high and operational troubles are likely to occur during coating. Furthermore, there is a tendency that the drying property of the ink is lowered. On the other hand, when the total amount of the adhesive is less than 5 parts by weight, it becomes difficult to obtain sufficient surface strength.

The coated paper for printing of the present invention preferably contains 10 to 80% by weight of the total adhesive and contains a styrene / butadiene copolymer latex in the form of an emulsion, and contains 15 to 70% by weight of latex. The latex preferably contains a styrene / butadiene latex. The coated paper for printing of the present invention comprises two or more pigment coated layers. The layer closest to the base paper preferably contains 10 to 80% by weight of latex in the total adhesive, and the layer far from the base paper has 30 to 30 layers. Preferably it contains 60% by weight latex. As other adhesives, it is particularly preferable to use starches, and the amount thereof is preferably 30 to 90% by weight in the total adhesive in the layer closest to the base paper, and 40 to 70% by weight in the layer far from the base paper. Preferably there is. Compared with latex, starches increase the water retention of the pigment coating liquid, so that the coating liquid is less likely to sink into the base paper, and the base paper can be effectively coated with the pigment coating layer. In other words, when starches are used, the coverage of the base paper by the pigment coating layer is improved. As a result, an improvement in printing quality, particularly printing glossiness, and an improvement in ink drying property can be expected. In the present invention, the ratio of latex to starch is preferably 3: 5 to 5: 7.

3) Other additives The pigment coating layer can be applied to ordinary coated paper pigments such as dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, dyes, and coloring pigments as necessary. Various auxiliaries to be blended may be included. In the present invention, it is preferable to use organic particles having a particle size larger than that of the aforementioned white pigment. By including the organic particles in the outermost coating layer farthest from the base paper, paper surface contamination due to rubbing between printed papers can be reduced, and printability can be improved. The organic particles are preferably non-steamed starch granules, and the above effect can be obtained by adding 0.5 to 10% by weight of the above-mentioned pigment. The organic particles preferably have an average particle size (D50) of 8 to 25 μm as measured with a laser diffraction particle size distribution analyzer.

4) Coating amount The coating amount of the pigment coating layer is preferably ² g / m ² or more, more preferably 5 g / m ² or more, and even more preferably 10 g / m ² or more in terms of solid content per side. If the coating amount is less than 5 g / m ² , the unevenness on the surface of the paper substrate cannot be sufficiently covered, and the acceptability of the printing ink may be significantly reduced. On the other hand, the coating amount of the pigment coating layer is preferably 50 g / ^{m 2} or less, more preferably ^{^{40g / m 2, 35g / m}} 2 or less is more preferred. The coating amount is a total value of all the pigment coating layers per side, but the coating amount of the innermost pigment coating layer (pigment coating layer adjacent to the base paper) is preferably 2 to 15 g / m ^2. More preferably, it is 5 to 12 g / m ² . The coating amount of the outermost pigment coating layer is preferably 6 to 20 g / m ² , more preferably 8 to 15 g / m ² . Since the influence of the outermost coating layer is large on the ink drying property, the coating amount of the outermost coating layer is preferably larger than the coating amount of the innermost pigment coating layer.

(2) Base paper 1) Pulp Known pulp can be used for the base paper. Known pulps include chemical pulp, groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), chemiground pulp (CGP), and semichemical pulp (SCP). And waste paper pulp. In the present invention, it is preferable to use chemical pulp. There are chemical pulps manufactured by the kraft pulp method and those manufactured by the sulfite pulp method, and both of them can be used in the present invention. From the aspect, it is preferable. The content of the chemical pulp in the raw material pulp is preferably 60% by weight or more, more preferably 80% by weight or more, still more preferably 90% by weight or more, particularly 95% by weight or more from the viewpoint of whiteness and the like. preferable.

2) Filler A known filler may be used for the base paper. Known fillers include heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, deramikaolin, white carbon, talc, magnesium carbonate, barium carbonate, barium sulfate, water Inorganic fillers such as amorphous silica produced by neutralization of aluminum oxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, sodium silicate with mineral acid, urea-formalin resin, melamine Organic fillers such as resin, polystyrene resin, phenol resin and the like. Among these, heavy calcium carbonate and light calcium carbonate, which are typical fillers for neutral papermaking and alkaline papermaking, are preferably used to improve opacity. The calcium carbonate used as the filler may be the first calcium carbonate or the second calcium carbonate described above, but light calcium carbonate is preferred. The filler content in the paper is not particularly limited, but is preferably 1 to 40% by weight, more preferably 10 to 35% by weight. Considering the strength of the base paper, it is more preferably 10 to 20% by weight.

3) Others Known paper additives can also be used. For example, sulfuric acid bands and various anionic, cationic, nonionic or amphoteric yield improvers, drainage improvers, various paper strength enhancers and internal additive sizing agents, etc. Can be used. Examples of the dry paper strength improver include polyacrylamide and cationized starch, and examples of the wet paper strength improver include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect the formation and operability. Examples of the internal sizing agent include alkyl ketene dimer, alkenyl succinic anhydride, and rosin sizing agent. Furthermore, dyes, pigments, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be added as necessary.

4) The basis weight of base paper coated printing paper having a basis weight of the present invention of the base paper is preferably 40 ~ 160g / ^{m 2,} more preferably 45 ~ 150g / ^{m 2,} more preferably 50 ~ 140g / ^{m 2.}

5) Clear coating layer The printing coated paper of the present invention may have a clear (transparent) coating layer on one side or both sides of the base paper described above. By performing clear coating on the base paper, the surface strength and smoothness of the base paper can be improved, and the coating suitability when applying pigment can be improved. The amount of the clear coating is preferably 0.1 ~ 3.0g / ^{m 2} by solid per side content, more preferably 0.2 ~ 2.0g / ^{m 2,} more preferably 0.5 ~ 2.0 g / a m ^2.

In the present invention, clear coating refers to, for example, a starch, oxidized starch, a coater (coating machine) such as a 2-roll pound size press, a gate roll coater, a pre-metering size press, a curtain coater, or a spray coater. Coating and coating liquids (surface treatment liquids) mainly composed of starches such as various modified starches (self-modified, cation-modified, etc.) and water-soluble polymers such as polyacrylamide and polyvinyl alcohol are coated on the base paper ( Size press). The clear coating liquid can be coated with a sizing agent. In the present invention, it is preferable to apply starch.

2. Production Method The coated paper for printing of the present invention can be produced by a known method, but it is preferably produced by applying a pigment coating solution containing a pigment and an adhesive on the base paper.
(1) Preparation of base paper The raw materials used for the base paper used in the present invention are as described above. The base paper is manufactured by a known paper making method. For example, use a long paper machine including top wire, on-top former, gap former, round paper machine, paperboard machine using a combination of long paper machine and round paper machine, Yankee dryer machine, etc. Can do. The pH during papermaking may be acidic, neutral or alkaline, but neutral or alkaline is preferred. The paper making speed is not particularly limited. The base paper used in the present invention may be a single layer or multiple layers, but a single layer base paper is preferably used.

(2) Smoothing treatment of base paper Before applying the pigment coating liquid to the obtained base paper, it is preferable to smooth the base paper with various calendar devices. As such a calendar device, a commonly used calendar device such as a super calendar or a soft calendar can be used as appropriate. As the calendar finishing conditions, the temperature of the rigid roll, the calendar pressure, the number of nips, the roll speed, the paper moisture before the calendar, and the like are appropriately selected according to the required quality. In the present invention, it is preferable to perform a calendar process on the base paper in order to impart smoothness while maintaining the matte texture. By applying a calendar treatment to the base paper, the smoothness of the base paper is improved and the pigment coating suitability is improved.

(3) Preparation of pigment coating liquid The pigment coating liquid can be prepared by dispersing or dissolving a pigment, an adhesive, and, if necessary, an additive in water. The composition of each component is adjusted so that the pigment coating layer can be formed. When performing blade coating, the solid content concentration of the pigment coating solution is preferably 40 to 70% by weight, more preferably 60 to 70% by weight. The viscosity of the pigment coating solution is preferably in the range of 500 to 5000 mPa · s as measured by the B-type viscosity measured at 60 rpm at room temperature. When coating is performed with a roll coater, the solid content of the pigment coating solution is preferably 50 to 70% by weight, more preferably 60 to 70% by weight. If the solid weight is too low, backflow or the like occurs, and if it is too high, the blade load increases and blade wear increases, which affects operability.

(4) Coating method The coating method is not limited, and known coating methods such as a roll coater and a blade coater can be used. The coating speed is not particularly limited, but is preferably 400 to 1800 m / min in the case of a blade coater and 400 to 2000 m / min in the case of a roll coater. In the present invention, the pigment coating layer may be applied with a single layer blade coater, may be applied with a roll coater and then applied with a blade coater, or may be applied with a blade coater and then applied with a blade coater. Although coating may be performed, since the smoothness of the surface can be improved, it is preferable to use a blade coater for coating the outermost coating layer.

In the coated paper for printing of the present invention, it is necessary to provide two or more pigment coated layers in order to increase the printing gloss. By providing two or more pigment coating layers, the fiber coverage is improved and the smoothness is also increased. When the number of layers is three or more, the coating amount can be increased, so that the quality of the coated paper is improved. However, the number of layers is preferably two from the viewpoint of cost and operability. As described above, a clear coating layer may be provided on the base paper, and two or more pigment coating layers may be provided thereon.

(5) Other steps The method for drying the wet coating layer is not limited. For example, a steam heating cylinder, a heated hot air air dryer, a gas heater dryer, an electric heater dryer, an infrared heater dryer, or the like can be used.

The coated paper for printing according to the present invention may be surface-treated as necessary with the coated paper produced as described above. However, since it is difficult to obtain the matte texture of the present invention, no calendar treatment is performed. It is desirable. When performing calendar processing, a commonly used calendar device such as a super calendar or a soft calendar can be used as appropriate. As the calender finishing conditions, the temperature of the rigid roll, the calender pressure, the number of nips, the roll speed, the paper moisture before the calender, etc. are appropriately selected according to the required quality, but in the coated paper for printing of the present invention In order to produce a matte texture, calendering at low pressure is preferable.

3. Paper quality (1) Blank paper glossiness Blank paper glossiness is an index indicating the glossiness of white paper, and is measured according to JIS-P8142 in the present invention. In one aspect, the coated paper for printing of the present invention is a coated paper for matte printing having a large difference between the glossiness of blank paper and the printed gloss. In this case, the glossiness of white paper is preferably 40% or less, more preferably 36% or less, and more preferably less than 32%. The lower limit of the white paper glossiness is not limited, but is preferably 15% or more.

(2) Print glossiness (Glossiness difference)
The print glossiness is an index indicating the glossiness of the printed material after printing, and is measured by the method described later in the present invention. In the matte coated coated paper for printing, the print glossiness (CM) is preferably 57 or more, more preferably 58% or more. The upper limit of the print glossiness in this case is not limited, but 75% or less is preferable. In the present invention, if the difference in glossiness obtained by subtracting the blank paper glossiness from the print glossiness is 15 or more, a sufficient difference in gloss between the printed portion and the blank paper portion is obtained, and it can be said that the printed matter is clearer. .

(3) Ink drying property The coated paper for printing of the present invention is excellent in ink drying property although the printing glossiness is high. The superiority or inferiority of the ink drying property of the coated paper for printing is generally identified by confirming the settling of the ink transferred to the other when the printed matter after printing is overlaid, or the rubbing stain on the printed surface.

(3-1) Evaluation by nitrogen adsorption method (total pore volume of paper) In the present invention, the pore structure of the pigment coating layer should be evaluated with a nitrogen adsorption method that can be measured under low pressure conditions. Thus, the ink drying property of the coated paper for printing of the present invention can be evaluated. Regarding the relationship between the pigment coating layer and the solvent absorptivity, the Lucas-Washburn formula shown in formula (1), in which a large number of fine pores existing in the pigment coating layer are regarded as aggregates of capillaries, is widely used. ing. Here, L is the penetration depth of the solvent, r is the average radius of the capillary, t is time, γ is the surface tension of the solvent, θ is the contact angle between the capillary wall and the solvent, and η is the viscosity of the solvent. Assuming that the cylindrical structure of the pigment coating layer has n cylindrical ridges having an average radius r, the ink solvent permeation amount ν into the pigment coating layer is expressed by Formula (2). (1) can be transformed as shown in equation (3). d is the thickness of the pigment coating layer, V is the pore volume of the pigment coating layer, and k is the viscosity of the ink. That is, it is considered that the larger the pore diameter and pore volume in the pigment coating layer, and the smaller the pigment coating layer thickness, the greater the amount of solvent permeation per fixed time and the more the ink drying property. In the present invention, the pore volume obtained by the Tristar 3000 is regarded as the pore volume of the pigment coating layer, and the average pore diameter is regarded as the average pore diameter of the pigment coating layer.

Pore volume V of the coated printing paper of the present invention is preferably 0.04 cm ³ / g greater, is more preferably 0.045 cm ³ / g or more. Preferably the upper limit is less than 0.09 cm ³ / g, more preferably 0.085cm ³ / g or less, and more preferably not more than 0.08 cm ³ / g. A coated paper for printing having a pore volume V higher than 0.04 cm ³ / g is excellent in ink drying property.

The total pore volume (cm ³ / m ² ) of the printing coated paper of the present invention is defined by pore volume V (cm ³ / g) × coating amount c (g / m ² ), and the value is 0.55 cm ³ / m ² or more is preferable, 0.60 cm ³ / m ² or more is more preferable, and 0.80 cm ³ / m ² or more is more preferable. The upper limit of the total pore volume is preferably 1.00 cm ³ / ^{m 2} or less, more preferably 0.95cm ³ / ^{m 2.}

The average pore diameter m of the coated paper for printing of the present invention is preferably 30 nm or more. The upper limit of the average pore diameter m is preferably 60 nm or less. Specifically, in the present invention, the average pore diameter is determined from a desorption isotherm obtained by a nitrogen adsorption method. In the present application, the average pore diameter obtained by the Tristar 3000 is regarded as the average pore diameter of the pigment coating layer.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Parts by weight and% by weight are values in terms of solid content.

<Evaluation method>
(1) Basis weight Measured according to JIS P 8124.
(2) ISO whiteness: measured in accordance with JIS P8148 using a color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd. under conditions including ultraviolet light.
(3) White paper glossiness Measured based on JIS-P8142.

(4) Ink drying property Ink density of solid part at a printing speed of 8000 sheets / hr using offset sheet-fed ink (NEX-M manufactured by Toyo Ink) with an offset sheet-fed printing machine (4 colors) manufactured by Roland. After printing so that the ink was 2.00, the solid black print portion was touched with a fingertip every 10 minutes immediately after printing, and the degree of ink drying speed was sensory evaluated.
A: Good B: Bad

(5) Printing glossiness (Glossiness difference)
Using offset sheet-fed ink (NEX-M manufactured by Toyo Ink Co., Ltd.) with an offset sheet-fed printing machine (4 colors) manufactured by Roland, the ink thickness of the solid part is indigo at a printing speed of 8000 sheets / hr. .60 and Crimson (CM) were printed in order of Crimson 1.50. The glossiness of the indigo red (CM) solid printed part of the obtained printed matter was measured based on JIS P-8142. The value obtained by subtracting the white paper glossiness from the printing glossiness is defined as the glossiness difference. If the glossiness difference is 15 points or more, the difference in glossiness between the printed portion and the white paper portion is sufficiently obtained, and it can be said that the printed matter looks good. .
Gloss level difference = printing gloss level (%)-blank paper gloss level (%)

(6) Pore volume etc. (i) Sample preparation and measurement The pore volume, total pore volume, and average pore diameter of the coated paper were determined by nitrogen adsorption method.
(Sample preparation)
A paper sample having a length of 40 cm and a width of 15 cm was divided into two layers so as to be uniform in the thickness direction to obtain a laminate including a pigment coating layer and a base paper layer. In the case of double-sided coated paper, two such laminates are obtained, and in the case of single-sided coated paper, one such laminate and one layer mainly composed of a base paper layer are obtained. A laminate including a pigment coating layer and a base paper layer was used as a sample sheet for measurement. In the case of double-sided coated paper, either one was used as a sample sheet for measurement. The basis weight t (g / m ² ) of the sample sheet was measured. Arbitrary four points in one sample sheet were selected, cut into strips, and then placed in a measurement cell so that the measurement sample had a dry weight of about 1 to 2 g. The absolutely dry weight at this time was set to w (g). Pretreatment was performed overnight in a vacuum state at a treatment temperature of 120 ° C.

(Measurement)
Using the apparatus, the pore volume and average pore diameter were measured from the pigment coating layer side of the measurement sample. Specifically, the pore volume and average pore diameter of the measurement sample were determined from the desorption isotherm using the BJH method, and the average value of four samples was taken, and the pore volume V ′ and average pore diameter of the measurement sample were taken. m ′. The pore volume V ′ was converted to a value per unit coating amount and used as the pore volume V of the pigment coating layer of the present invention. The obtained average pore diameter m ′ was directly used as the average pore diameter m of the pigment coating layer of the present invention. The pigment coating layer weight of the measurement sample is: pigment coating layer weight (g) = absolute dry weight w (g) of measurement sample × coating amount c (g / m ² ) ÷ basis weight t (g / g of sample sheet) m ² ). The coating amount c (g / m ² ) was determined by the measurement method described later. For the measurement and analysis, Tristar 3000 manufactured by Shimadzu Corporation was used.

(Coating amount)
The coating amount was measured according to the method described in Japanese Patent No. 5827187. Specifically, it measured by the following procedures.
1) A measurement sample (paper) was cut into a size of 5 cm × 5 cm, and the weight x after humidity adjustment was measured at a temperature of 23 ° C. and a relative humidity of 50%.
2) The sample was placed so that the pigment coating layer was in contact with the styrene polymer plate, and was sandwiched with a watch glass and fixed with a clip.
3) Put into a dryer at 120 to 150 ° C., melt the styrene polymer, adhere to the pigment coating layer, allow to cool, adjust the humidity at about 23 ° C. and 50% relative humidity for about half a day, and measure the weight y. .
4) After the measurement sample obtained in the previous step was immersed in a copper ethylenediamine solution for about 3 to 4 hours, the base paper layer and the pigment coating layer were carefully peeled off using a brush. This process was repeated until there was no pulp fiber adhering to the pigment coating layer.
5) The pigment coating layer was washed with water and dried. After conditioning for about half a day at a temperature of 23 ° C. and a relative humidity of 50%, the weight z was measured.
6) The coating amount was calculated by the following formula.
Coating amount c (g / m ² ) = (x−A) × 400
A = yz

[Example 1]
A base paper having a basis weight of 75 g / m ² containing 13.5% by weight of light calcium carbonate as a filler was prepared using 100% by weight of chemical pulp.
100 parts by weight of heavy calcium carbonate (trade name: FMT97, D50 = 0.88 μm) made of heavy calcium carbonate as a pigment, 7 parts by weight of styrene / butadiene copolymer latex as an adhesive, and oxidized starch 3 parts by weight was added, and water was further added to obtain an undercoat pigment coating solution having a solid concentration of 65% by weight.
Heavy calcium carbonate as a second calcium carbonate (manufactured by Phymatech Co., Ltd., trade name: FMT97, D50 = 0.88 μm) as a pigment and 55 parts by weight of heavy calcium carbonate as a first calcium carbonate (Co., Ltd.) 45 parts by weight (manufactured by Pfematec, trade name: FMT100, D50 = 0.66 μm), 4 parts by weight of styrene / butadiene copolymer latex and 6 parts by weight of oxidized starch as an adhesive, and water Was added to obtain a topcoat pigment coating solution having a solid content concentration of 66% by weight.
On the base paper, an undercoat pigment coating solution was coated on both sides with a blade coater so that the dry coating amount per side was 6.5 g / m ² and dried. Further, a top coat pigment coating solution was coated on both sides with a blade coater so that the dry coating amount per side was 10.5 g / m ² , thereby obtaining a coated paper for printing. The coated paper for printing was evaluated by the method described above.

[Example 2]
97 parts by weight of self-made causticized light calcium carbonate (D50 = 1.38 μm) and 3 parts by weight of self-made causticized light calcium carbonate (D50 = 1.02 μm) are used as pigments, and styrene / butadiene copolymer latex as an adhesive. 2.5 parts by weight and 21 parts by weight of oxidized starch were added, and water was further added to obtain an undercoat pigment coating solution having a solid content concentration of 50% by weight.
44.5 parts by weight of self-made fine causticized light calcium carbonate (D50 = 0.64 μm) as the first calcium carbonate as a pigment and 55 self-made causticized light calcium carbonate (D50 = 1.02 μm) as the second calcium carbonate 4 parts by weight of styrene / butadiene copolymer latex and 6 parts by weight of oxidized starch, and uncooked starch granules (trade name: Y-3P, manufactured by Cornstarch Japan) are used. 0.5 parts by weight was added, and water was further added to obtain a topcoat pigment coating solution having a solid content concentration of 66% by weight.
On the base paper, the undercoat pigment coating solution was coated on both sides with a gate roll coater so that the dry coating amount per side was 4.5 g / m ² and dried. Further, a top coat pigment coating solution was coated on both sides with a blade coater so that the dry coating amount per side was 10.5 g / m ² , thereby obtaining a coated paper for printing. The coated paper for printing was evaluated by the method described above.

[Example 3]
Starch that has not been cooked, with the amount of the first calcium carbonate, styrene-butadiene copolymer latex, and oxidized starch blended in the topcoat pigment coating solution prepared in Example 1 changed to the amounts shown in Table 1 A top coat pigment coating solution containing 0.5 parts by weight of granules (trade name: Y-3P, manufactured by Nippon Corn Starch Co., Ltd.) was prepared. A coated paper for printing was produced and evaluated in the same manner as in Example 1 except that the coating liquid was used.

[Example 4]
100 parts by weight of heavy calcium carbonate (trade name: FMT90, D50 = 1.15 μm) as a pigment, 7 parts by weight of styrene / butadiene copolymer latex as an adhesive, and oxidized starch 3 parts by weight was added, and water was further added to obtain an undercoat pigment coating solution having a solid concentration of 70% by weight.
55 parts by weight of heavy calcium carbonate (made by Imeris, trade name: C90, D50 = 1.18 μm) as the second calcium carbonate as a pigment, and fine heavy calcium carbonate (made by Imeris, Carbilax) as the first calcium carbonate , D50 = 0.64 μm) 44.5 parts by weight, 4 parts by weight of styrene / butadiene copolymer latex and 6 parts by weight of oxidized starch as an adhesive, and uncooked starch granules (Nippon Corn Starch Co., Ltd.) (Product name: Y-3P) was added in an amount of 0.5 parts by weight, and water was further added to obtain a topcoat pigment coating solution having a solid concentration of 66% by weight. Using these coating solutions, printing coated paper was produced and evaluated in the same manner as in Example 1.

[Comparative Example 1]
85 parts by weight of heavy calcium carbonate (trade name: FMT75, D50 = 1.65 μm) as a pigment, 15 parts by weight of kaolin (trade name: KCS, D50 = 4.05 μm, manufactured by Imeris), As an adhesive, 4.3 parts by weight of styrene / butadiene copolymer latex and 6.5 parts by weight of oxidized starch were added, and water was further added to obtain a pigment coating liquid having a solid content concentration of 66% by weight. Using the coating solution, a coated paper for printing having one pigment coating layer was produced in the same manner as in Example 1, and evaluated.

[Comparative Example 2]
Heavy calcium carbonate (trade name: C97, D50 = 0.91 μm) 100 parts by weight as a pigment, 7.6 parts by weight of styrene-butadiene copolymer latex and 6 parts by weight of oxidized starch as an adhesive Then, water was added to obtain a pigment coating solution having a solid content concentration of 66% by weight. Using the coating solution, a coated paper for printing having one pigment coating layer was produced in the same manner as in Example 1, and evaluated.

[Comparative Example 3]
As a pigment, 55 parts by weight of heavy calcium carbonate (manufactured by Phymatech Co., Ltd., trade name: FMT97, D50 = 0.88 μm), 45 parts by weight of kaolin (trade name: KCS, D50 = 4.05 μm, manufactured by Imeris Corporation), As an adhesive, 4 parts by weight of styrene / butadiene copolymer latex and 6 parts by weight of oxidized starch were blended, and water was further added to obtain a pigment coating solution having a solid content concentration of 66% by weight. Using the coating solution, a coated paper for printing having one pigment coating layer was produced in the same manner as in Example 1, and evaluated.

[Comparative Example 4]
55 parts by weight of heavy calcium carbonate (trade name: FMT97, D50 = 0.88 μm) as a pigment and fine heavy calcium carbonate (trade name: FMT100YF, D50 = 0.08 μm). 60 μm) 45 parts by weight, 4 parts by weight of styrene / butadiene copolymer latex as an adhesive and 6 parts by weight of oxidized starch were added, and water was added to obtain a pigment coating solution having a solid content concentration of 66% by weight. . Using the coating solution, a coated paper for printing having one pigment coating layer was produced in the same manner as in Example 1, and evaluated.

It is clear that the coated paper for printing of the present invention has an excellent balance between ink drying properties and printing gloss.

Claims

Two or more pigment coating layers are provided on at least one side of the base paper,
A coated paper for printing, wherein the outermost pigment coating layer contains calcium carbonate having an average particle size (D50) of 0.80 μm or less.
The coated paper for printing according to claim 1, wherein 40 parts by weight or more of the calcium carbonate is contained in 100 parts by weight of the pigment in the outermost pigment coating layer.
The coated paper for printing according to claim 1 or 2, wherein the calcium carbonate has an average particle diameter (D50) of 0.50 to 0.75 µm.
The coated paper for printing according to any one of claims 1 to 3, wherein the glossiness of the white paper is 40% or less and the printing glossiness of the indigo printing portion is 58 to 75%.
The coated paper for printing according to claim 2, wherein 75 parts by weight or more of the calcium carbonate is contained in 100 parts by weight of the pigment in the outermost pigment coating layer.
The coated paper for printing according to any one of claims 1 to 5, wherein the coating amount of the outermost pigment coating layer is larger than the coating amount of the innermost pigment coating layer.